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Strabismus 

What is strabismus (also called squint)?

Eyes that point in different directions or are misaligned have a condition called strabismus. Different types of strabismus include:​

  • Crossed eyes (esotropia)

  • Out-turned eyes (exotropia)

  • Vertical misalignment, in which one eye is higher or lower than the other (hyper- or hypotropia)
     

The problem may be present at all times (constant) or may only appear at certain times, such as when the eyes are tired (intermittent). If left untreated, these patients suffer from a loss of binocular vision and stereopsis, which means that the two eyes do not work together as they should to provide depth perception. Many can have a limitation of their field of vision (peripheral vision or side vision). There can even be a loss of central vision—called amblyopia or lazy eye. Strabismus in adults is usually the result of progressive, untreated, or unsuccessfully treated childhood strabismus. Sometimes, strabismus develops in adults following an injury or illness and causes double vision.

How is strabismus treated?

Treatment options depend upon the type of strabismus; however all types follow a three-step approach:

  1. Eliminate the underlying cause if possible

  2. Correct the reduced vision (amblyopia) that results

  3. Attempt to restore the normal alignment (straighten the eyes) by operating on the external eye muscles.

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The sooner the treatment is begun, the more likely the eyes will be properly realigned without developing amblyopia. Some types of strabismus can be treated with glasses and other types can only be corrected by surgery. Strabismus that develops early in childhood and is constant needs to be corrected surgically.

Why surgery?

Surgery for turned eyes aims to improve the alignment of the eyes so that they "look straight" and to encourage or restore the ability of the brain to use the eyes together “binocular vision”. It can often also increase peripheral vision and sometimes increase depth perception. 

What alternatives are there to surgery?

  • Glasses

  • Patching

  • Orthoptic exercises (occasionally)

  • Prisms in glasses

  • Botox injections

  • Do nothing (i.e. leaving the squint alone)

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These alternatives should have been discussed and tried (if appropriate) before undertaking squint surgery. If you feel you do not understand the place of alternative treatment, please ask.

When not to operate?

  • If you are unwilling to accept the risks associated with squint surgery outlined below

  • If you do not understand why the operation is being done or do not understand the risks involved

  • If the chance of improving the alignment of the eyes is low

Risks of squint operation

  • Ongoing misalignment – The operation may not produce the desired effect (that is the eyes are not well aligned). The magnitude of this risk varies with age and the type of squint that is present. In virtually all cases this problem can be treated by undertaking another squint operation.

  • Ongoing double vision – This operation aims to decrease the frequency of double vision but it is impossible to eliminate double vision in all positions of eye movement.

  • Recurrence of misalignment – The squint may recur after the operation. 1 in 3 people who have squint surgery as a child will need a further squint operation during their life. In about 1 in 500 - 1,000 cases this problem occurs because the stitch(es) used to reattach the muscles to the eye loosen. In many cases it is due to the brain being unable to use the two eyes together.

  • Infections are uncommon. About 1 in 150 experience a mild surface infection (conjunctivitis) that will require topical antibiotic eye drops to settle. More serious infection at the site of the surgery, in the socket or in the eye itself is very rare.

  • Loss of sight following a squint operation is extremely rare occurring in 1 in 20,000 cases.

  • Problems with wound healing occur occasionally (1 in 100 - 200). This may be evident as a pink lump (granuloma) or white strand of tissue (prolapsed connective tissue). These problems usually settle without any specific treatment. Rarely an operation is required to remove the lump. Rarely there may be a small visible scar or cyst at the site of the operation.

Risks of general anaesthesia 

  • The risks related to the general anaesthesia should be discussed with the anaesthetist on the day of surgery. The anaesthetic plan is designed to minimise risk and distress.

  • The risk of serious harm occurring during the course of an elective general anaesthetic is extremely low (of the order of 1 in 200,000).

  • Transient problems, e.g. sore throat, bruise at IV site, contribution to nausea and vomiting, getting upset, etc are more common.

  • If you have other significant medical problem these risks may change. The significance of general conditions should be discussed with your anaesthetist.

What does strabismus surgery involve?

Once you are asleep the skin around the eyes and the surface of the eye is cleaned with disinfectant (Betadine). The eyelids are then held apart with a small clamp and the eye rotated so that the muscle that is to be operated on is accessible. The tissue (conjunctiva) over the white of the eye is then cut open with scissors to expose the muscle and then the muscle is either weakened or strengthened. The muscle is reattached to the eye wall with a suture (thread). The opening in the conjunctiva may or may not be sutured. This process is repeated for each muscle that is operated on. Eyes are not “removed” to realign them, it is just the eye muscles that are moved to weaken or change their action or shortened to strengthen them.

After your operation

After your operation you will be provided detailed information on what to expect during the recovery process. Medication/eyedrops will be prescribed with instructions for aftercare. A follow-up appointment date will be arranged for generally one day after and a second appointment for approximately a month after. 

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